The Respiratory System Flashcards
What is COPD?
• Chronic obstructive pulmonary disease (COPD) is the name for a group of lung conditions that cause breathing difficulties.
It includes:
• emphysema - damage to the air sacs in the lungs
• chronic bronchitis - long-term inflammation of the airways
• 3rd leading cause of death worldwide, causing 3.23 million deaths in 2019. In the UK its effects around 3 million people, with 2 million of these being undiagnosed and 1,151,474 people diagnosed in England (2024) and slightly more common in men than in women.
• COPD is not curable but symptoms can improve if one avoids smoking and exposure to air pollution and gets vaccines to prevent respiratory infections.
Emphysema
• Emphysema develops over time and involves the gradual destruction of the alveoli
• Gradually, this damage causes the air sacs to rupture and create one big air pocket instead of many small ones.
• This reduction in the lung surface area traps air in the damaged tissue
• The damaged alveoli don’t work properly and old air becomes trapped, leaving no room for fresh, oxygen-rich air to enter
Chronic Bronchitis
• Bronchitis is inflammation of the breathing tubes (bronchi).
• This causes a narrowing of the airways and excess mucus production.
• Again, no cure but treatments can help manage the condition
Causes of COPD
A combination of risk factors:
• Tobacco exposure from active smoking or passive exposure to second-hand smoke
• Occupational exposure to dusts, fumes or chemicals
• Indoor air pollution: biomass fuel (wood, animal dung, crop residue) or coal is frequently used for cooking and heating in low- and middle-income countries with high levels of smoke exposure
• Early life events such as poor growth in utero, prematurity, and frequent or severe respiratory infections in childhood that prevent maximum lung growth
• Asthma in childhood
• Genetic factors are also thought to increase risk
Symptoms of COPD
Common:
• Shortness of breath – this may only happen when exercising at first, sometimes wake up at night feeling breathless
• A persistent chesty cough with phlegm that does not go away for more than 3 months
• Frequent chest infections
• Persistent wheezing
• The symptoms will usually get gradually worse over time and make daily activities increasingly difficult
Less common:
• Weight loss
• Tiredness
• Swollen ankles from a build-up of fluid (oedema)
• Chest pain and coughing up blood – although these are usually signs of another condition, such as a chest infection or possibly lung cancer
Link to clinical observations
• Heart Rate
• Respiration Rate
• SPO2
• General level of consciousness and interaction with you
• Temperature of core vs extremities and colour
Diagnosis (NHS NICE)
• Diagnosis of COPD is based on the presence of typical clinical features supported by spirometry.
• COPD should be suspected in people aged over 35 years, who have a risk factor and symptoms including exertional breathlessness, chronic/recurrent cough, or regular sputum production.
• A post bronchodilator ratio of forced expiratory volume in 1 second to forced vital capacity (FEV1/FVC) of less than 0.7 on spirometry confirms persistent airflow obstruction.
• Investigations (including chest X-ray and full blood count) should be arranged to exclude other causes of symptoms.
• NB - post bronchodilator means after medication has been given Bronchodilator medicines relax the muscles in the lungs and open the airways. This makes breathing easier
Technical terms
• FEV1 – Forced Expiratory Volume in one second
• FVC – Forced Vital Capacity
• FEV1/FVC ratio – the outcome of the test (as a decimal or %)
Treatments
• Inhalers (Short and long term and combination inhalers)
• Steroids
• Lifestyle changes to promote self-care and better health
• Pulmonary rehabilitation
• Surgery
Trachea
• The primary function of the trachea is to allow passage of inspired and expired air into and out of the lungs.
• The trachea is 16 to 20 C-shaped cartilage rings stacked one on top of another. A narrow thin membrane connects each of the tracheal rings.
• The trachea has four layers of which two are important to know
• The inner mucosal layer has a lining of ciliated tissue with goblet cells that produce mucus
• The outer cartilage layer is sturdy but flexible and prevents the collapse of the trachea during expiration
Ciliated tissue in the trachea/ bronchi
• The bronchus in the lungs are lined with hair-like projections called cilia that move microbes and debris up and out of the airways.
• Scattered throughout the cilia are goblet cells that secrete mucus which helps protect the lining of the bronchus and trap microorganisms.
• The first defensive barrier to infection and damage in the lungs and airways is provided by the action of mucus and cilia
. They act together to trap microorganisms and particles, and move them out of the lungs prior to disposal (by coughing or swallowing)
Bronchi/bronchioles
The function of the bronchi and bronchioles is to distribute the air throughout the lungs until reaching the
respiratory bronchioles and alveolar sacs
Bronchioles lack cartilage in their walls and rely on smooth muscle and elastic fibres to maintain their wall integrity. The smooth muscle is also important to control airflow through contraction and dilation of the airway.
Club cells in the bronchioles form surfactant which aid bronchioles to expand during inhalation and avoid bronchial collapse during exhalation
Types of pneumocytes
• Type 1 – thin cells that are adapted to carry out gas exchange. Most cells in the alveoli are type 1 cells that are flat to minimise the distance that gases have to diffuse between the capillary and the alveoli – about 0.5um – this adaptation increases rate of gas exchange
• Type 2 - secrete a solution called surfactant that creates a moist surface inside the alveoli to prevent the side of the alveolus adhering to each other. They are about 5% by surface area of the alveoli. This thin layer creates a film of moisture that supports diffusion of gases
Pulmonary surfactant
• The fluid secreted by type 2 cells is ‘pulmonary surfactant’. Surfactants are substances that reduce surface tension.
• Its molecules have a similar structure to that of phospholipids in cell membranes but only one layer, not two.
• They form a layer on the surface of the moisture lining with hydrophilic heads facing the water and hydrophobic tails facing the air.
• This reduces surface tension and stops the lungs form collapsing due to the pressure changes during breathing, supports elasticity and contains proteins that support immunity.
Remember
• it is the strength of the concentration gradient that drives gas exchange.
Factors that increase diffusion:
• A short distance
• A strong gradient
• Temperature
• Surface area of type I pneumocytes is high
• Once Oxygen has diffused across the alveolar and capillary membranes, it combines with haemoglobin. This forms oxyhaemoglobin
Specialisations of the alveoli for gas exchange
• large surface area to volume ratio (type 1 cells)
• good blood supply
• short diffusion distance
• moisture levels
• body temperature
Haemoglobin and gas exchange
• The haemoglobin molecule is made of four polypeptides that are structured with a haem group (with an iron ion) making four haem groups per red blood cell.
• This means that each cell can carry four oxygen molecules from the lungs as oxyhaemoglobin
• Haemoglobin is able to change is shape in the presence of substances such as carbon dioxide so the molecules of oxygen are bound more loosely which results in its release from the cell
Transport of CO2 in the body
Carbon dioxide molecules are transported in the blood from body tissues to the lungs by one of three methods:
• dissolution directly into the blood 5-7%
• binding to haemoglobin 10%
• carried as a bicarbonate ion 83-85%
• This is linked to the bicarbonate buffer system which has a role in maintaining blood pH as well as providing a speedy transfer of carbon dioxide back into the blood
Bicarbonate Buffer System
• Carbon dioxide diffuses into the red blood cells. Carbonic anhydrase (CA) within the red blood cells quickly converts the carbon dioxide into carbonic acid (H2CO3)
• Carbonic acid is an unstable intermediate molecule that immediately dissociates into bicarbonate ions (HCO−3) and hydrogen (H+) ions. This process maintains blood pH at 7.35-7.45.
CO2+H2O ⟷ H2CO3 ⟷ HCO3+H+
(Carbon dioxide + water) (carbonic acid) (bicarbonate +hydrogen ion)
The mechanics of breathing
Inspiration:
• Diaphragm contracts – moves down – low pressure draws air inwards
• External intercostal contract – rib cage up and outwards
Exhalation:
• Elastic recoil of the tissue of the lungs
• Diaphragm relaxes and moves up – increases pressure so forcing air out of the lungs
• External intercostals relax - rib cage moves in and down
process of inhalation and exhalation
• During inhalation air is drawn into the lungs due to the low pressure created by the contraction of the diaphragm which moves downwards and the intercostal muscles contract which forces the chest upwards and outwards.
• During exhalation air is expelled by the lungs due to the higher pressure created when the diaphragm relaxes which moves upwards and the intercostal muscles relax causing the chest to move inwards and down
